Known cell separation methods from body fluids operate as a rule by means of filtration, centrifugal force or sedimentation. For this purpose a number of methods and apparatuses have been developed. The majority of these methods is based on the problem of freeing liquids from particles (water processing) and then removing the liquid. In this process the purified fluid or liquid is used again and the particles are discarded. In such methods, particle recovery from the filters used, for example multilayer or depth-type filters, is also not possible.
In laboratory medicine in the investigation of body fluids very different methods are employed each governed by the diagnostic objective or clinical picture. It is known to centrifuge fluid specimens for recovering cells. The sediment is then evaluated via microscopic slide smears. In accordance with the prior art preferably a specific type of centrifugation is employed in which the cell material is deposited from an introduced specimen directly on a microscope slide. The (body) fluid in this process is separated from the particles via the centrifugation process and collected in a fleece paper which is clamped together with the microscope slide in the centrifuge.
Apart from centrifugation methods for cell recovery filtration methods are also employed which are based mainly on membrane filter technology.
If pathological processes, for example neoplasia, are to be detected in body fluids, for example urine the cells relevant to the cytological diagnosis must be isolated in great number and without selection from the overall specimen. The cytologist then makes particularly high demands of the investigation material and the cell recovery method. It is very important here that after recovery of the cells their original state is fully retained, i.e. that the fine morphology of the cells corresponds to the state which they had already during the exfoliation from the tissue into the fluid. In the case of body fluid specimens this is usually material made up in very different ways. Ascites is frequently rich in cells, blood and protein and has a high viscosity. Female urines are richer in cells and more viscous than male urines. Inflammatory processes contaminate the specimens with erythrocytes and leucocytes and also influence the flow rate. Specimens can equally well be mixed with protein, fibrin and blood coagulant. Bacteria destroy cells and lead to permeation of the specimens with detritus.
For cytology of body fluids, and this applies apart from urine to all such fluids as well as to liquor, effusions, ascites and peritoneal cavity lavage, irrespective of the nature of the fluid it must be possible to recover a well preserved cell material.
Known methods used for particle and/or cell recovery still have disadvantages. Thus, it is known that in centrifugation processes a comparatively large amount of cell material can be lost at the walls of the centrifuge glasses, depending on the adhesion behaviour of the cells.
Known membrane filters also have considerable disadvantages; in particular, they cannot be employed for specimens very rich in cells or for highly viscous solutions. Sensitive or predamaged cells are destroyed or modified to a great extent in both methods. Also disadvantageous are filtration methods and apparatuses in which cells are lost. For this falsifies the overall picture of the cytological preparation and there is a danger that small-cell carcinomas are negatively selected.
Known medical diagnostic methods make the following demands of a cell recovery method and the associated apparatuses, although as a rule these demands cannot be met or can be met only incompletely;
Separation of all the cells important for the diagnosis without cell selection or cell loss.
No restriction as regards the particle size. Cells with diameters of 7 .mu.m and less must be acquired to an equal extent to cell conglomerates with more than 100 .mu.m diameter.
The viscosity of a solution (of body fluid) must not have any influence on the recovery rate of the cells.
The method must be quick, effective and operate reproduceably as well as being suitable for mass examinations.
To protect the user it must be ensured that any contact with the fluid to be investigated by a person carrying out the test is largely excluded (infection prophylaxis).
After separation of the particles it must be possible to safely dispose of the fluid specimen or to keep it safely in a closed system for other tests.
Finally, it should be possible to fix or conserve particles (cells) separated from the fluid directly after the recovery in a suitable liquid, for example alcohol.